Better error message if `abi` is not provided for contract

[pipermerriam]

• Version: 3.x and 4.x

What was wrong?

In 3.x if no ABI is provided when instantiating a contract instance you would get an unhelpful error message as seen here: #696

In 4.x this type of error won't occur, however, the situation can still be approved because the contract.functions API simply won't have any accessible functions.

How can it be fixed?

I don't think we need to fix 3.x but we could provide a simple patch to raise a better error message if self.abi is None.

In 4.x I think that we can improve the situation. Maybe accessing contract.functions when abi is None should raise an exception that no contract ABI was provided (same for accessing contract.events).

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Work has been started.

1. @nemaniarjun (1st precedence)
2. @watonyweng (2nd precedence)
3. @mikery (3rd precedence)

has committed to working on this project to be completed 5 months, 3 weeks from now.

[nemani]

Hey! I am new to Gitcoin, Web3 and blockchain in general. I do have python coding experience and I think I can get this done.

For 3.x : Add an Exception with a proper message here

For: 4.x: This is bit more complex, on my first go through the code, I think raising exceptions on creation of ContractFunction and ContractEvent Class objects should be enough.

I see for testing, PyTest is being used, I will write tests for the changes I make :)

Please let me know if this plan seems suitable, I will start reading the docs and more about web3.py, web3.js and Ethereum in general.

[pipermerriam]

Yes, feel free to take this on.

For 4.x (which is master) the best I can think of is to raise a custom AttributeError when an attempt is made to access a function via c.functions.myFunction in the case where the abi contains no function definitions.

>>> c.functions.myFunction
AttributeError("The abi for this contract contains no function definitions.  Are you sure you provided the correct contract abi?")

[mikery]

I would like to take a shot at this. The approach in PR #800 will raise an exception if you instantiate a contract with no ABI, but I think the behaviour we want is to only raise an exception if an attempt is made to access a non-existent function/event. PR incoming.

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Issue Status: 1. Open 2. Started 3. Submitted 4. Done

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Issue Status: 1. Open 2. Started 3. Submitted 4. Done

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